I would like to think that we do have some fake diversity in this game with the few units that Relic wont make useful and takes up space.
Like the SU-76, what is that even for...
It was ment as light at and ai vehicle that you can use before going for su-85 and katy while going t4. And it even served that role in the early stages of the game. I remember winning matches in 1v1 by building 2-3 su-76 before ostheer could get any tanks becaoude of map control that gave you. Still it needed some serious skills to use, but relic decided it is op and nerfed both su-76 and its tier by increasing fuel cost. From that patch nobody uses it as it shows up too late to be usefull couse it is hard countered by p4.
To sum up: it is a great unit, and it's well placed in t4 but it needs cost reduction to about 60-65 fuel to make sense.